Threat behavior
TrojanDropper:Win32/Nuwar.A is a Trojan that drops and installs Backdoor:Win32/Nuwar.A or Backdoor:Win32/Nuwar.B onto an infected computer.
Backdoor:Win32/Nuwar is a Backdoor Trojan that allows unauthorized access to an infected computer. The Trojan receives commands indirectly from a remote attacker via its connection to a malicious peer-to-peer network. This Trojan also contains advanced stealth functionality that allows it to hide particular files, registry entries and registry values.
When executed, Backdoor:Win32/Nuwar peforms the following actions:
Creates a configuration file <system>\wincom32.ini which contains a list of peers to connect to initially (see 'Backdoor Functionality' section below for further detail).
Drops a kernel driver <system>\wincom32.sys which is then installed, using the file name (minus the extension) as the display name (as in wincom32) - this driver is detected as Backdoor:Win32/Nuwar!sys
Creates a mutex named 'E8dK894Lm9#sF2i$sOBq2X', which it uses as a marker to prevent re-installation attempts if the driver is already running.
Injects a malicious payload into "services.exe". The consequence of this action will make any network activity appear to originate from services.exe.
Attempts to modify 'Windows Time' configuration settings.
Note: <system> refers to a variable location that is determined by the malware by querying the Operating System. The default installation location for the System directory for Windows 2000 and NT is C:\Winnt\System32; and for XP and Vista is C:\Windows\System32.
Advanced Stealth Features
The driver, wincom32.sys, hides files, registry keys and registry values beginning with the string 'wincom32' by hooking the following functions:
NtEnumerateKey
NtEnumerateValueKey
NtQueryDirectoryFile
Backdoor Functionality
The component that was injected into services.exe attempts to join a P2P network, where directives can be exchanged between like peers. Once connected to the network, active peers can be instructed to download and execute arbitrary files.
Related Malware
Prevention